The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to propellant formulations and plastic bonded explosive compositions. More particularly, this invention relates to energetic compositions, which offer increased performance in conjunction with a total absence of hydrogen chloride in the combustion products.
State-of-the-art propellant formulations, at their most basic level, are composed of an oxidizer and a fuel. The combustion reaction undergone by these two materials provides the energy necessary to propel the rocket or missile. Since the oxidizer/fuel combination must sustain the stresses of handling, aging, storage and use, it is typically compounded in a formula consisting of binder, plasticizer and various solid ingredients. Ideally, all the components in the formulation act as either oxidizers or fuels, contributing to the energy necessary for maximum propulsion performance, although in practice, certain necessary ingredients such as stabilizers and burn rate catalysts/modifiers, have little or no energy to impart to the reaction.
The performance of the propellant is directly proportional to the enthalpy release of the oxidizer and fuel ingredients as they undergo combustion, and inversely proportional to the molecular weight of the gases produced in the combustion reaction. In practice, some tradeoffs are necessary to gain the best performance from available ingredients and formulations. Aluminum, for instance, is a fuel whose combustion products are relatively high in molecular weight, and are in most cases, not gases at all, but solids. However, the enthalpy release by the combustion of aluminum is so great in proportion to anything else, which would otherwise be available as a fuel ingredient, that the metal is commonly used as a fuel in high-performance tactical and strategic rocket motor applications. Another material commonly utilized, despite some drawbacks, is the oxidizer ammonium perchlorate. This material has a high negative enthalpy of formation, limiting its energy release upon combustion, and, in addition, it produces hydrogen chloride upon combustion, a relatively high-molecular-weight toxic gas. However, ammonium perchlorate is inexpensive, easy to formulate, has very tractable ballistics and favorable burn characteristics, and so, despite its limitations, it is the state-of-the-art oxidizer for most solid propellant rocket motor formulations.
Ammonium dinitramide (ADN) is a very powerful inorganic oxidizer that can replace ammonium perchlorate (AP) in propellant compositions. Calculations have shown that, when incorporated in propellant formulations, the propellant can achieve performance equal to or higher than that of the conventional hydroxyl-terminated polybutadiene (HTPB)/AP propellant. Most desirably, ADN propellants do not produce toxic, high-molecular-weight hydrogen chloride (HCl) in the exhaust. In addition, the use of ADN in propellant formulations greatly minimizes the secondary smoke problem caused by the nucleation of HCl. Because of their environmentally friendly characteristics and demonstrated reduced toxicity of their exhaust products to humans, ADN propellants are highly desirable. In recent years, investigators have been designing propellant formulations that try to embody the advantages of ADN as a solid oxidizer.
The need to have missiles fly farther, higher and faster, and to carry heavier payloads is a constant tactical and strategic factor. Higher performance is always needed. In volume-limited systems, this performance can only come about by increases in the quantity, density or energy of the propellant formulation, by decreases in the weight of the inert hardware and the airframe, and by operating at higher pressures. A new requirement has come to light in recent years: that the formula and its combustion products be nondegrading to the environment. In the light of these requirements, state-of-the-art propellant formulations utilizing conventional binders, ammonium perchlorate and aluminum have been developed and refined to the maximum extent possible and these compositions will necessarily begin to fall behind in performance compared to newer developments. In addition, the political and environmental concerns with the toxic and corrosive hydrogen chloride present in the exhaust of rockets utilizing these formulations will result in demands to replace such formulations with more innocuous compositions. Below, a propellant formulation, which is a solution for both problems, is disclosed.
The solid propellant formulations disclosed herein exhibit superior properties without the negative environmental impact of existing propellants.
One object of a preferred embodiment of the present invention is to provide a solid propellant formulation comprising about 5 to about 10 weight % of at least one energetic binder; about 20 to about 35 weight % of an energetic plasticizer; about 25 to about 45 weight % of ammonium dinitramide as a primary oxidizer; about 0 to about 20 weight % of particulate aluminum having a particle size of about 1 xcexcm to about 60 xcexcm; and about 0 to about 20 weight % of particulate aluminum having a particle size of less than 1 xcexcm. In addition to the ingredients in this basic formulation will be cure catalysts, curatives, crosslinkers, burn rate catalysts and modifiers, thermal and aging stabilizers, opacifiers and other such ingredients commonly utilized in solid propellant formulations.
One object of a preferred embodiment of the present invention is to provide a solid rocket propellant, which offers increased performance in conjunction with a total absence of hydrogen chloride in the combustion products.
Another object of a preferred embodiment of the present invention is to provide a solid rocket propellant, which eliminates halogen-containing compounds from the combustion products while maintaining good performance and good mechanical properties.
A still further object of a preferred embodiment of the present invention is to provide a solid propellant formulation, which utilizes ADN as an oxidizer to greatly minimize the secondary smoke problem caused by the nucleation of HCl in AP.